Primitive Archer
Main Discussion Area => Horn Bows => Topic started by: loon on August 22, 2016, 08:51:15 pm
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I've been planning on making a jig for fixing my hornbow's twist..
Will heat from the horn (belly) side, also have an infrared thermometer, may take it up to 48C or so , and then heat the whole bow to 40C?
Should I take a video of the top limb while drawing it to find out where the twist is, and then try to correct it.. it looks like it's mostly the upper 1/3 of the sal/bending limb but begins a bit below the middle of the sal. Should probably try to take picturs/video perfectly frontal as well ...
The top limb's ear is also tracking to the right viewed from the back from when I tried to correct it..
(http://i.imgur.com/12cOqLD.png)
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I can see that.Not much though really.It doesnt throw the string off though correct?You got Adam's instructions on that procedure.
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I can see that.Not much though really.It doesnt throw the string off though correct?You got Adam's instructions on that procedure.
Thanks
Yeah it doesn't (almost seems to) but I can tell the siyah is really not in line more easily at brace
Adam Karpowicz? I only saw text about twist correction, no pretty pictures, and I didn't see anything about using special jigs to correct twist or offset. I don't recall if he mentioned that it should be heated from the horn side, which I noticed in Adam Swoboda's book
(http://i.imgur.com/4TyBf4l.jpg)
Sorry about the crappy drawing. This is what I'm planning to do... dowels or pegs in a pine board. Instead of wrapping for the supports, I could put on blocks of wood. but hopefully wrapping would work fine. Was thinking either twisting twine or using a clamp to apply force
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Forget the jigs!
You can easily correct that twist by hand. Simply heat then over correct and hold there until cool. Then leave it for a few hours before stringing it. Check for twist again and repeat if necessary.
Hornbows just don't lend themselves to jigs and clamping etc.
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Yes Adam Karpowicz's book.Heating limb at the twisted area from the horn side not over 50 degrees centigrade.He used little heart blankets at times for more control of temp.Using a heat gun will work too[waving it slowly back and forth] letting the heat slowly penetrate but then I moniter temp with a laser temp gun too.Then like what Mike mentioned over correcting and holding till cool.All by hand.You'll see results.Your almost there and done I'd be patient and don't do anything drastic now.....lol.Look forward to seeing the final bow done.
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Yes I forgot to add that...be very careful not to overheat it! Better for it to take a few attempts than get it too hot once.
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Thanks Mike and Beadman!!
I hope I didn't overheat it already when I didn't have an infrared thermometer. From the sinew side, no less. Though I nearly took it to full draw... (this is few days ago, haven't done anything yet), and that area doesn't really bend much
(https://i.imgur.com/wA9Di1i.png)
Good to hear that I don't need to sweat making any jigs. I thought I would because I could give it propeller twist otherwise, which it doesn't seem to have..
old pic, pretty sure it is different now but not that much (just the ear should lean to the right more now)
(https://img0.etsystatic.com/116/0/56955725/icm_fullxfull.87055870_i0myll8yje0o0w4g40k4.jpg)
P.S. this bow is from Tc.. stringing with tepeliks in the floor is hard and I screwed it up, hence this twist. Shipping back and forth from Hungary is too expensive.
I've still got a long way to go before I start making hornbows :P
I'll just make one of those Korean style bracing things, or just put the teplik on my vise at first.
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Bow is quite wide though - 42x11mm ~ 1 2/3" x 3/7", so it seems rather hard to bend it sideways, especially the maple core
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I see.It's ok if the tips look out of line a little at rest.Just so it's dead nuts at brace and full draw.
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Your gaining on her.You'll make it.
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I put it lightly on a vise, heated it until the reader registered 46-50C and pressed it down against the side of a pine board, hands on mid-limb and at the knee and the pine board in between for a little, pressing from the side.. about how much force should be used?
Maybe next time I'll try a more twisting motion
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pictures
Yup. Unbalance..
(https://s25.postimg.org/7lizww2f3/CIMG0303.jpg)
(https://s25.postimg.org/8p348un27/CIMG0304.jpg)
(https://s25.postimg.org/eejct5t8f/CIMG0305.jpg)
(https://s25.postimg.org/f5c2yxvlr/CIMG0306.jpg)
I should make some leather strips for the kemend or whatever. May have to heat the other limb.. wouldn't that make it stronger though? The top limb is the weak one that I've heated. While unstrung, of course.
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putting on tepeliks on the floor
and... it's the exact same bow.. Kurszan.
https://www.youtube.com/watch?v=FovttGwdLdE
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If one limb is stronger than the other simply squeeze the string into the weaker limbs belly thus putting more strain on the weaker. Make sure you keep the string centered as you squeeze. You can also cut a section out of an inner tube (like a thick rubber band). Don't heat the sals with the bow strung.
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If one limb is stronger than the other simply squeeze the string into the weaker limbs belly thus putting more strain on the weaker. Make sure you keep the string centered as you squeeze. You can also cut a section out of an inner tube (like a thick rubber band). Don't heat the sals with the bow strung.
I do that and I also put the knee on it and pull with one hand on the tip and another on the knee to balance. That top limb just really wants to be weaker..
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With heat + twisting, the chance of delamination is high.
I was thinking of clamping it on the vise at the handle, maybe clamping part of the limb, heating a smallish section to 45 or so and twisting at the ear opposite to the twist (rather than just pressure on the side..).
Of course, putting towels or cardboard at the clamping points..
My area is rather dry of course.
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No it isn't! You may think so but the only way you will damage it by heating/twisting is by either heating it too much or by putting a silly amount of pressure on it. Clamping is more likely to damage it.
If the corrections haven't held then either you relaxed the pressure before it cooled or you didn't get it hot enough. Heat gently for plenty of time.
Also remember that the maker would have balanced it one limb relative to the other when making it - you are trying to get that balance back. I strongly recommend you don't remove any material. to make the upper limb weaker. Tillering horn bows is quite different to wooden bows where the default action to weaken a limb is to remove material on a hornbow that is the last resort.
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"Also pay attention if you use heat and twisting - the danger of delamination is high." - Tc
A lot of bowyers use clamps when gluing up horn bows, though.. so I thought it'd be the same sort of thing
I think this is definitely true if too much heat is applied or in a humid climate, apparently hide glue liquifies more easily with higher humidity..
I'm thinking of just balancing it by pressing and then leaving it for a few hours with tepeliks on, or maybe with those straps you slip on (kemend?)
Though this kind of thing also looks good to maintain balance
(https://i.imgur.com/qnjOlyy.jpg)
I wish I had more time for all this. Maybe next year I can make revenue by selling arrows or something O_o
Thanks for replying
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These things are all relative....How much twisting, how much heat etc....this is the problem with computers and internet knowledge! Haha! If we were face to face and had the bow I could show you how to sort it out in a few minutes and there would be no confusion,crossed wires or terminology problems ;)
Just stick at it. Be gentle, patient and don't get it too hot. I guess what I am saying is don't overthink it your bow can be corrected with simple heat and pressure. The magic in tillering hornbows is in making them stable and a lot of the ability to do that comes with practise and feel.
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thanks
I applied a lot of force, waited an hour and the twist is somewhat reduced but still there... limb has a bit of an S shape. It's hard to bend much of anything just with bare hands, especially the siyah I think, strangely enough. Pictures later. 1:33am and I have to get up for work at 5:20am or so ugh.
I think for siyah misalignment (I really screwed up the siyah when trying to adjust twist with clamps and stuff..) Adam mentioned clamping the ear to a table??
I took it to 29", heard a few tics but it didn't blow up!??
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It has barely changed, though I guess balance is a bit better now.
Previously, I used this sort of jig to try to fix the twist. A bit more heat and pressure than I can by hand. Now I can't undo the offset on the top limb's ear. (edit - kind of managed just by adjusting when the bow was strung)
recommended
(https://i.imgur.com/9RusoAB.png)
actual (I screwed up the ear by putting the center pressure point with that giant old clamp at the knee)
This was how it should've actually been - the twist appears to start mid-limb
This was months ago.
(https://i.imgur.com/jpgMCKXl.jpg)
But whatever, it shoots. Although I guess it'd be significantly better without twist. Shot a few times with a 700 grain arrow with 29" draw (planned on 50 but got tired after 8 or so, only reached full draw on two). A tad of handshock, I guess the leather absorbs a little bit.
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I think it makes sense to just make a video showing the bow from many angles..
(https://s25.postimg.org/6ylxcv1a3/CIMG0337.jpg) (https://s25.postimg.io/xjog8f3nj/CIMG0337.jpg)
(https://s25.postimg.org/3t1bmninv/CIMG0338.jpg) (https://s25.postimg.io/dqccfpq9r/CIMG0338.jpg)
(https://s25.postimg.org/8g7dof60r/CIMG0339.jpg) (https://s25.postimg.io/us56ht54v/CIMG0339.jpg)
(https://s25.postimg.org/605kakny3/CIMG0340.jpg) (https://s25.postimg.io/purlwp35r/CIMG0340.jpg)
(https://s25.postimg.org/mpblk89x7/CIMG0341.jpg) (https://s25.postimg.io/jv8g6s7r3/CIMG0341.jpg)
(https://s25.postimg.org/gpnugkp4r/CIMG0342.jpg) (https://s25.postimg.io/3lia3vx33/CIMG0342.jpg)
(https://s25.postimg.org/65dwxzkmz/CIMG0344.jpg) (https://s25.postimg.io/cj3018pj3/CIMG0344.jpg)
(https://s25.postimg.org/ggq9qnccb/CIMG0345.jpg) (https://s25.postimg.io/w27laloan/CIMG0345.jpg)
(https://s25.postimg.org/a4b4gt9a3/CIMG0346.jpg) (https://s25.postimg.io/nxzh5v1vj/CIMG0346.jpg)
(https://s25.postimg.org/g6ir7axq3/CIMG0351.jpg) (https://s25.postimg.io/lhxns0jsv/CIMG0351.jpg)
What I fear is that shooting this bow with twist would put the limbs onto uneven stress and twist it further
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I apologize for the shakiness, hopefully it's obvious enough.
https://www.youtube.com/watch?v=HxvzKqauXUA
seem to have fixed ear twist a bit just by cold pulling holding handle & ear and knee on bow knee somewhat hard and holding just after stringing the bow
considerable bending limb twist..
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It's taken a while.. I'm slow
Walnut for tepeliks?
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I want to get new tepeliks made. Maybe walnut or butternut.. or a softer maple? I don't know what wood the Koreans use. Think I want one set of thick ones for bracing on the floor, and another of thinner ones to use one of those Korean benches.
Trying to fix twist... and the sinew damage. I don't know why it's black, if it's debris or voids or something. Used alcohol, then coated it with thin, then thick hide glue. I'll wrap it with sinew later. Blurry.. because I am so damn shaky. I should use my tripod.
(https://i.imgur.com/tMq3NdG.jpg)
(https://i.imgur.com/Hpie0bdl.jpg)